Image-forming devices such as laser printers include tandem color image-forming devices that are well known in the art, such as that disclosed in Japanese unexamined patent application publication No. 2003-015378. These types of image-forming devices have a plurality of detachably mounted developer cartridges for supplying developer to the surfaces of respective photosensitive drums.
The developer cartridge generally includes a casing for accommodating developer, and a developing roller rotatably supported in the casing for carrying developer supplied within the casing. An elongated opening is formed in the casing so that a portion of the surface of the developing roller is exposed therethrough and opposes the surface of the photosensitive drum. The developing roller carries developer from the casing on the surface thereof. As the developing roller rotates, the developer carried on the surface of the developing roller comes into contact with the surface of the photosensitive drum and is supplied to the electrostatic latent image formed on the surface of the photosensitive drum. The developer develops the electrostatic latent image into a developer image, and the developer image is subsequently transferred onto a sheet of paper, thereby forming an image on the paper.
In this type of developer cartridge, a side seal is provided on both ends of the developing roller in order to prevent developer from leaking between the ends of the developing roller and the casing.
Japanese unexamined patent application publication No. 2001-60040 proposes fixing a safeguard film formed of PET film on the lower front edge of the casing in the developer cartridge at the front part of the side seals. With this construction, even if developer leaks from the developer cartridge, the safeguard film can minimize the damage caused by such leakage.